Rotary printing presses including varnishing devices and dryers that are arranged after the varnishing devices are known from the prior art. The dryers dry the printing material that has been varnished in the varnishing devices is dried, are known from the prior art. Thus, for example, in sheet-fed rotary offset presses, the sheets that have been printed in the printing units are covered with a varnish layer in a varnishing unit that is connected after or downstream of the printing units. The sheets are subsequently guided past a known dryer device in the form of an infrared, hot-air or UV dryer, in which the varnished sheets are dried before being deposited on a deliverer stack. The purpose of known varnishing units is increasing the rubbing resistance and the gloss of printed products or preventing ink from being deposited in the stack in the event of a very thin application of varnish. The varnishing is usually performed in the final printing units.
A free inking unit can be the simplest way to varnish printed products. In such a case, as is known, a special heat-set ink is used that can be processed like a normal heat-set ink. The special heat-set ink is transferred onto the surface of the paper wet-on-wet together with the printing ink and then dried in heat-set dryers. Special varnishing units are also available to meet the ever-increasing quality requirements associated with web-fed offset printing. The special varnishing units are positioned between the final printing unit and the heat-set dryer. Varnishing operations can be performed with aqueous emulsion varnishes. Most emulsion varnishes are dried through physical evaporation of the water. However, in web-fed offset printing, a special UV drying system (UV radiant heater) can be used that is capable of performing not only the drying of the printing ink, but also partial UV varnishing. Special UV varnishes that are applied to 100% polymerizable binder constituents are used.
Inkjet technology is in widespread use in both home PC printers as well as industrial applications such as digital proof systems that use the data of an ESP system directly with digital printers. For the home and office, a wide variety of printer manufacturers are known that are capable of producing relatively high-quality (generally >1200 dpi), multi-color prints. Such printers are usually designed for personal use. In other words, the printers are actuated by a PC and can be used with a variety of printing materials. The disadvantages of home and office printers generally include slow printing speeds (low number of printed copies per unit time) and the relatively high cost of the printing inks. As will be appreciated, home/office inkjet printers are not suitable for industrial applications.
Inkjet printing systems for industrial printing applications are also known. For example, inkjet systems can be used to produce proofs, to set images on printing plates or printing forms. Inkjet systems can also be used for digitally printing small special runs (for example, printing structural shapes) and special formats (for example, large-format posters or textiles). In a similar manner to home/office inkjet printing applications, industrial applications predominantly use inkjet printing systems for very small print runs and that the costs for printing inks are very high. As compared to conventional printing methods such as offset and gravure, inkjet printing is not economical for printing large runs, as inkjet printing is very slow at high print resolutions (>1200 dpi). At low print resolutions (<300 dpi), inkjet printing is capable of providing a relatively high number of printed copies per unit time, but at the expense of satisfactory print quality.
Up to now, coating, varnishing or finishing of conventionally printed products (for example, offset or gravure printed products) or of digitally printed products (for example, photo-electric printing) has been performed using conventional coating, varnishing or finishing methods, as has been described above. These can be methods for flexographic printing, gravure printing or offset printing. Additionally, there are coating methods that are performed by means of lamination (for example, adhesive bonding of films or other carrier materials). These methods are likewise used predominantly for finishing and to protect the surface of the printed products.
As also discussed above, water-based varnishes and UV varnishes are mainly used when varnishing printed products. The varnishing procedures can be performed over the entire area or only on sub-areas. In such a case, conventional coating methods are particularly suitable for large print runs and high quality requirements.